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Counterion influence on dynamic spin properties in a V(iv) complex.

ABSTRACT: Using transition metal ions for spin-based applications, such as electron paramagnetic resonance imaging (EPRI) or quantum computation, requires a clear understanding of how local chemistry influences spin properties. Herein we report a series of four ionic complexes to provide the first systematic study of one aspect of local chemistry on the V(iv) spin - the counterion. To do so, the four complexes (Et₃NH)₂[V(C₆H₄O₂)₃] (1), (n-Bu₃NH)₂[V(C₆H₄O₂)₃] (2), (n-Hex₃NH)₂[V(C₆H₄O₂)₃] (3), and (n-Oct₃NH)₂[V(C₆H₄O₂)₃] (4) were probed by EPR spectroscopy in solid state and solution. Room temperature, solution X-band (ca. 9.8 GHz) continuous-wave electron paramagnetic resonance (CW-EPR) spectroscopy revealed an increasing linewidth with larger cations, likely a counterion-controlled tumbling in solution via ion pairing. In the solid state, variable-temperature (5-180 K) X-band (ca. 9.4 GHz) pulsed EPR studies of 1-4 in o-terphenyl glass demonstrated no effect on spin-lattice relaxation times (T ₁), indicating little role for the counterion on this parameter. However, the phase memory time (T _m) of 1 below 100 K is markedly smaller than those of 2-4. This result is counterintuitive, as 2-4 are relatively richer in ¹H nuclear spin, hence, expected to have shorter T _m. Thus, these data suggest an important role for counterion methyl groups on T _m, and moreover provide the first instance of a lengthening T _m with increasing nuclear spin quantity on a molecule.

SUBMITTER: Lin CY

PROVIDER: S-EPMC6335635 | biostudies-literature | 2019 Jan

REPOSITORIES: biostudies-literature

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Counterion influence on dynamic spin properties in a V(iv) complex.

Lin Chun-Yi CY Ngendahimana Thacien T Eaton Gareth R GR Eaton Sandra S SS Zadrozny Joseph M JM

Chemical science 20181018 2

Using transition metal ions for spin-based applications, such as electron paramagnetic resonance imaging (EPRI) or quantum computation, requires a clear understanding of how local chemistry influences spin properties. Herein we report a series of four ionic complexes to provide the first systematic study of one aspect of local chemistry on the V(iv) spin - the counterion. To do so, the four complexes (Et3NH)2[V(C6H4O2)3] (1 ...[more]

PMID: 30746097

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Project description:The influence of carbon black (CB) structure and surface area on key rubber properties such as monotonic stress-strain, cyclic stress-strain, and dynamic mechanical behaviors are investigated in this paper. Natural rubber compounds containing eight different CBs were examined at equivalent particulate volume fractions. The CBs varied in their surface area and structure properties according to a wide experimental design space, allowing robust correlations to the experimental data sets to be extracted. Carbon black structure plays a dominant role in defining the monotonic stress-strain properties (e.g., secant moduli) of the compounds. In line with the previous literature, this is primarily due to strain amplification and occluded rubber mechanisms. For cyclic stress-strain properties, which include the Mullins effect and cyclic softening, the observed mechanical hysteresis is strongly correlated with carbon black structure, which implies that hysteretic energy dissipation at medium to large strain values is isolated in the rubber matrix and arises due to matrix overstrain effects. Under small to medium dynamic strain conditions, classical strain dependence of viscoelastic moduli is observed (the Payne effect), the magnitude of which varies dramatically and systematically depending on the colloidal properties of the CB. At low strain amplitudes, both CB structure and surface area are positively correlated to the complex moduli. Beyond ~2% strain amplitude the effect of surface area vanishes, while structure plays an increasing and eventually dominant role in defining the complex modulus. This transition in colloidal correlations reflects the transition in stiffening mechanisms from flexing of rigid percolated particle networks at low strains to strain amplification at medium to high strains. By rescaling the dynamic mechanical data sets to peak dynamic stress and peak strain energy density, the influence of CB colloidal properties on compound hysteresis under strain, stress, and strain energy density control can be estimated. This has considerable significance for materials selection in rubber product development.

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Counterion influence on dynamic spin properties in a V(iv) complex.

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Counterion influence on dynamic spin properties in a V(iv) complex.

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